The present invention relates to fiber optic sensors, and particularly to a stabilized, all fiber, resonant ring interferometric sensor.
Optical fibers are sensitive to a large number of ambient effects, such as acoustic waves and temperature fluctuations. The ambient quantities acting upon the optical fiber can result in changes in the amplitude, phase, or polarization of light propagating therethrough. Consequently, there has recently been a great deal of interest in the use of fibers as sensor elements.
Mach-Zehnder and Sagnac interferometers are commonly used as sensors. In these interferometers, the phase difference between interfering light waves varies in response to the variations in sensed quantity, and thus, by detecting the intensity of light produced by such interfering waves, the magnitude of the sensed quantity can be determined. In addition, the detected intensity varies as a function of the cosine of the phase difference between the light waves. Typically, the interferometer is biased to operate at the point of maximum slope on such cosine curve, the sensed quantity being detected by measuring fluctuations in intensity from this operating point. However, the maximum slope of a cosine curve is about 1/2 radians.sup.-1, assuming a peak-to-peak optical power normalized between zero and one. Thus, the sensitivity of these devices is limited. Further, since a cosine curve becomes very non-linear towards its minima and maxima, only a portion of the curve is generally usable for linear measurements.